Physiological roles of the light, oxygen, or voltage domains of phototropin 1 and phototropin 2 in Arabidopsis1

Cho, H.-Y., Tseng, T.S., Kaiserli, E., Sullivan, S. , Christie, J.M. and Briggs, W.R. (2007) Physiological roles of the light, oxygen, or voltage domains of phototropin 1 and phototropin 2 in Arabidopsis1. Plant Physiology, 143(1), pp. 517-529. (doi: 10.1104/pp.106.089839)

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Phototropins (phot1 and phot2) are plant blue-light receptors that mediate phototropism, chloroplast movement, stomatal opening, rapid inhibition of growth of etiolated seedlings, and leaf expansion in Arabidopsis (<i>Arabidopsis thaliana</i>). Their N-terminal region contains two light, oxygen, or voltage (LOV) domains, which bind flavin mononucleotide and form a covalent adduct between a conserved cysteine and the flavin mononucleotide chromophore upon photoexcitation. The C-terminal region contains a serine/threonine kinase domain that catalyzes blue-light-activated autophosphorylation. Here, we have transformed the <i>phot1 phot2 (phot1-5 phot2-1</i>) double mutant with <i>PHOT</i> expression constructs driven by the cauliflower mosaic virus 35S promoter. These constructs encode either wild-type phototropin or phototropin with one or both LOV-domain cysteines mutated to block their photochemistry. We selected multiple lines in each of the eight resulting categories of transformants for further physiological analyses. Specifically, we investigated whether LOV1 and LOV2 serve the same or different functions for phototropism and leaf expansion. Our results show that the LOV2 domain of phot1 plays a major role in phototropism and leaf expansion, as does the LOV2 domain of phot2. No complementation of phototropism or leaf expansion was observed for the LOV1 domain of phot1. However, phot2 LOV1 was unexpectedly found to complement phototropism to a considerable level. Similarly, transformants carrying a <i>PHOT</i> transgene with both LOV domains inactivated developed strong curvatures toward high fluence rate blue light. However, we found that the <i>phot2-1</i> mutant is leaky and produces a small level of full-length phot2 protein. In vitro experiments indicate that cross phosphorylation can occur between functional phot2 and inactivated phot1 molecules. Such a mechanism may occur in vivo and therefore account for the functional activities observed in the <i>PHOT</i> transgenics with both <i>lov</i> domains inactivated. The implications of this mechanism with respect to phototropin function are discussed.

Item Type:Articles
Glasgow Author(s) Enlighten ID:Kaiserli, Dr Eirini and Christie, Professor John and Sullivan, Dr Stuart
Authors: Cho, H.-Y., Tseng, T.S., Kaiserli, E., Sullivan, S., Christie, J.M., and Briggs, W.R.
Subjects:Q Science > QK Botany
College/School:College of Medical Veterinary and Life Sciences > School of Molecular Biosciences
Journal Name:Plant Physiology
ISSN (Online):1532-2548
Published Online:01 November 2006

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